【BZOJ2466】【中山市选2009】树 高斯消元解异或方程组

广告：

#include <stdio.h>int main(){    puts("转载请注明出处[vmurder]谢谢");    puts("网址：blog.csdn.net/vmurder/article/details/44356273");}

题解：

参照此题解，也是我写的，俩题一样。
【POJ1681】Painter’s Problem 高斯消元，求最小∑系数的异或方程组

代码：

#include <cmath>#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#define N 105#define inf 0x3f3f3f3fusing namespace std;bool a[N][N],x[N];int crs[N],n,ans;void dfs(int id,int which,int now){    if(id<1)    {        ans=min(ans,now);        return ;    }    if(now>=ans)return ;    if(crs[id]==which)    {        bool ret=a[id][n+1];        for(int i=which+1;i<=n;i++)ret^=(a[id][i]*x[i]);        x[which]=ret;        dfs(id-1,which-1,now+ret);    }    else {        x[which]=true;        dfs(id,which-1,now+1);        x[which]=false;        dfs(id,which-1,now);    }    return ;}int Gauss(int n,int m){    int i,j,k,id;    for(id=i=1;i<n;i++,id++)    {        for(j=id;j<=m&&!a[j][i];j++);        if(j>m){id--;continue;}        crs[id]=i;        if(id!=j)for(k=i;k<=n;k++)swap(a[id][k],a[j][k]);        for(j=id+1;j<=m;j++)if(a[j][i])for(k=i;k<=n;k++)            a[j][k]^=a[id][k];    }    for(i=id;i<=m;i++)if(a[i][n])return -1;    return id-1;}int id[N][N],cnt;char src[N];void init(){    cnt=0,ans=inf;    memset(a,0,sizeof a);    memset(x,0,sizeof x);    memset(id,0,sizeof id);    memset(crs,0,sizeof crs);}int main(){    freopen("test.in","r",stdin);    int i,j,k;    int x,y,t;    while(scanf("%d",&n),n)    {        init();        for(i=1;i<n;i++)        {            scanf("%d%d",&x,&y);            a[x][y]=a[y][x]=1;        }        for(i=1;i<=n;i++)a[i][i]=a[i][n+1]=1;        t=Gauss(n+1,n);        if(t==-1)puts("inf");        else {            dfs(t,n,0);            printf("%d\n",ans);        }    }    return 0;}